Paracord tensioner - used to mount sunshade as outlined here.
Modeled this version from scratch, based on the STL found here. Which is apparently based on something called a Loop Alien. Or probably a knockoff Loop Alien, which was then adapted as a 3D-printed device. Wild how things develop. This is released as public domain with CAD files. Enjoy.
See the video (not mine) below for how to use it, and ALSO how you can actually do this sort of tightening operation without any extra hardware, just knots:
Perhaps it should go without saying, but this is NOT A SAFETY RATED DEVICE. Use at your own risk.
The author marked this model as their own original creation.